1. Field of the Invention
The present invention relates to an objective lens driving device. More specifically, the invention relates to a technical field of an objective lens driving device that performs a focusing adjustment and a tracking adjustment on an objective lens by moving a biaxial movable body with respect to a recording medium such as an optical disc.
2. Description of the Related Art
Optical disc apparatuses capable of recording and/or reproducing a signal on and/or from an optical disc are known. These optical disc apparatuses are equipped with an objective lens driving device that performs a focusing adjustment and a tracking adjustment on an objective lens by moving a biaxial movable body with respect to a recording medium such as an optical disc.
FIG. 1 shows an example of such a conventional objective lens driving device.
The objective lens driving device a has a biaxial movable body b and four magnetic circuits c and d.
The biaxial movable body b is configured in such a manner that a portion e to be supported and a lens holding portion f that projects from the portion e in one direction are formed integrally with each other. The central portion of the portion e is supported by a support shaft g so as to be slidable in its axial direction and rotatable about the axis. Two focusing coils h are provided on the outer periphery of the portion e so as to be opposed to each other with the support shaft g interposed in between, and two tracking coils i are similarly provided on the outer periphery of the portion e to be supported so as to be opposed to each other with the support shaft g interposed in between. The focusing coils h and the tracking coils i are arranged alternately.
An objective lens j is held on the top surface of the lens holding portion f.
Magnets k are disposed so as to be opposed to the focusing coils h and the tracking coils i, respectively. The magnets k are attached to respective yoke pieces 1.
The focusing coils h, the two magnets k, the two yoke pieces 1, and neutral iron pieces (not shown) that are provided to occupy central portions of the respective focusing coils h constitute two first magnetic circuits c, which move the biaxial movable body b in the axial direction of the support shaft g and thereby perform a focusing adjustment on the objective lens j with respective to the optical disc.
The tracking coils i, the two magnets k, the two yoke pieces 1, and neutral iron pieces (not shown) that are provided to occupy central portions of the respective tracking coils i constitute two second magnetic circuits d, which move the biaxial movable body b about the axis of the support shaft g and thereby perform a tracking adjustment on the objective lens j with respective to the optical disc.
However, the above conventional objective lens driving device a is equipped with the two first magnetic circuits c for the focusing adjustment and the two second magnetic circuits d for the tracking adjustment, that is, the four magnetic circuits c and d in total. Since the magnetic circuits c and d need to be disposed outside the biaxial movable body b, the objective lens driving device a becomes larger when the number of magnetic circuits is larger.
Further, the number of parts that constitute the objective lens driving device increases in proportion to the number of magnetic circuits, causing increase in manufacturing cost.
An object of the present invention is to solve the above problems.
To attain the above object, the invention provides an objective lens driving comprising a biaxial movable body that is supported by a support shaft so as to be slidable in an axial direction of the support shaft and rotatable about the support shaft; an objective lens held by the biaxial movable body; a plurality of focusing coils that are provided on the biaxial movable body so as to be symmetrical with respect to the support shaft; a tracking coil or coils that are provided on the biaxial movable body in a number that is smaller than the number of focusing coils; and magnets that are opposed to the focusing coils and the tracking coil or coils, respectively, wherein a plurality of first magnetic circuits are formed by the focusing coils and part of the magnets that are opposed to the respective focusing coils; and second magnetic circuit or circuits are formed by the tracking coil or coils and the other magnet or magnets that are opposed to the tracking coil or coils, respectively, in a number that is smaller than the number of first magnetic circuits. The objective lens is driven by the magnetic circuits having the above focusing coils and tracking coil or coils.